Nonvolatile semiconductor memory device

ABSTRACT

A nonvolatile semiconductor memory device according to an embodiment includes: a semiconductor layer; a block insulating film; an organic molecular layer, which is formed between the semiconductor layer and the block insulating film, and provided with a first organic molecular film on the semiconductor layer side containing first organic molecules and a second organic molecular film on the block insulating film side containing second organic molecules, and in which the first organic molecule has a charge storing unit and the second organic molecule is an amphiphilic organic molecule; and a control gate electrode formed on the block insulating film.

CROSS-REFERENCE TO RELATED APPLICATION

This divisional application is based upon and claims the benefit ofpriority under 35 U.S.C. §120 from U.S. application Ser. No. 13/934,784,filed Jul. 3, 2013, which claims the benefit of priority from U.S.Provisional Application No. 61/767,433, filed on Feb. 21, 2013, theentire contents of each of which are incorporated herein by reference.

FIELD

Embodiments described herein generally relate to a nonvolatilesemiconductor memory device.

BACKGROUND

As a method for realizing reduced bit cost of a nonvolatilesemiconductor memory device and also enhancing memory performancethereof, scaling down of a memory cell is promising. However, scalingdown of the memory cell has become technically difficult.

It has thus been proposed to use organic molecules for a charge storinglayer. Because, various organic molecules can be formed by organicallysynthesize a variety of molecular structures and substituent groups,desired electrochemical properties can be applied to the organicmolecules. And constitutional unit of the organic molecules is small.Therefore, the organic molecules may realize further scaling-down of thememory cell. In realizing the scaling-down of the memory cell, it is ofimportance to improve qualities of a block insulating film and a controlgate electrode, formed on the charge storing layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of a memory cell unit of a nonvolatilesemiconductor memory device according to a first embodiment;

FIG. 2 is a circuit diagram of a memory cell array of the nonvolatilesemiconductor memory device according to the first embodiment;

FIG. 3 is an enlarged sectional view of the memory cell unit of thenonvolatile semiconductor memory device according to the firstembodiment;

FIGS. 4A to 4D are diagrams each exemplifying a molecular structure of acharge storing unit according to the first embodiment;

FIG. 5 is a diagram exemplifying a molecular structure of the chargestoring unit according to the first embodiment;

FIG. 6 is a diagram exemplifying a molecular structure of the chargestoring unit according to the first embodiment;

FIG. 7 is a diagram exemplifying a molecular structure of a secondorganic molecule according to the first embodiment;

FIG. 8 is a structural diagram of an organic molecular layer accordingto the first embodiment;

FIG. 9 is a structural diagram of the organic molecular layer accordingto the first embodiment;

FIG. 10 is a sectional view of a memory cell unit of a nonvolatilesemiconductor memory device according to a second embodiment;

FIG. 11 is a sectional view of a memory cell unit of a nonvolatilesemiconductor memory device according to a third embodiment;

FIG. 12 is a sectional view of a memory cell unit of a nonvolatilesemiconductor memory device according to a fourth embodiment;

FIG. 13 is a sectional view of a memory cell unit of a nonvolatilesemiconductor memory device according to a fifth embodiment;

FIG. 14 is a three-dimensional conceptual diagram of each of thenonvolatile semiconductor memory devices according to sixth and seventhembodiments;

FIG. 15 is an X-Y sectional view of the nonvolatile semiconductor memorydevice of FIG. 14 according to the sixth embodiment;

FIG. 16 is an X-Z sectional view of the nonvolatile semiconductor memorydevice of FIG. 14 according to the sixth embodiment;

FIG. 17 is an X-Y sectional view of the nonvolatile semiconductor memorydevice of FIG. 14 according to the seventh embodiment;

FIG. 18 is an X-Z sectional view of the nonvolatile semiconductor memorydevice of FIG. 14 according to the seventh embodiment;

FIG. 19 is a diagram showing a molecular structure of a first organicmolecule described in Example;

FIG. 20 is a diagram showing results of capacitance measurementsdescribed in Example; and

FIG. 21 is a diagram showing temporal changes of capacitances of Exampleand Comparative Example.

DETAILED DESCRIPTION

A nonvolatile semiconductor memory device according to an embodimentincludes: a semiconductor layer; a block insulating film; an organicmolecular layer which is formed between the semiconductor layer and theblock insulating film and provided with a first organic molecular filmcontaining first organic molecules on the semiconductor layer side and asecond organic molecular film containing second organic molecules on theblock insulating film side, and in which the first organic molecule hasa charge storing unit and the second organic molecule is an amphiphilicorganic molecule; and a control gate electrode formed on the blockinsulating film.

Hereinafter, embodiments will be described with reference to thedrawings.

First Embodiment

A nonvolatile semiconductor memory device according to the presentembodiment includes a semiconductor layer, a block insulating film, andan organic molecular layer formed between the semiconductor layer andthe block insulating film. The organic molecular layer is provided witha first organic molecular film containing first organic molecules on thesemiconductor layer side, and a second organic molecular film containingsecond organic molecules on the block insulating film side. The firstorganic molecule has a charge storing unit, and the second organicmolecule is an amphiphilic organic molecule. The memory device furtherincludes a tunnel insulating film formed between the semiconductor layerand the organic molecular layer.

In the nonvolatile semiconductor memory device according to the presentembodiment, a high-quality block insulating film can be realized byprovision of the above configuration. This leads to improved insulationproperties between the charge storing unit and the control gateelectrode, thereby to improving data retention properties. This alsoleads to an improved reliability of the block insulating film.

FIG. 1 is a sectional view of a memory cell unit of the nonvolatilesemiconductor memory device according to the present embodiment. FIG. 2is a circuit diagram of a memory cell array of the nonvolatilesemiconductor memory device according to the first embodiment. Thenonvolatile semiconductor memory device of the present embodiment is anNAND nonvolatile semiconductor memory device.

As shown in FIG. 2, for example, the memory cell array is made up ofmemory cell transistors MC₁₁ to MC_(1n), MC₂₁ to MC_(2n), . . . , andMC_(m1) to MC_(mn), as m×n (m and n are integers) transistors having afloating-gate structure. In the memory cell array, these memory celltransistors are arrayed in a column direction and in a row direction;and a plurality of memory cell transistors are thereby arranged in amatrix form.

In the memory cell array, for example, the memory cell transistors MC₁₁to MC_(1n) and select gate transistors STS₁ and STD₁ areseries-connected, to form an NAND string (memory string) as a cell unit.

A drain region of the select gate transistor STS₁ for selecting thememory cell transistors MC₁₁ to MC_(1n) is connected to a source regionof the memory cell transistor MC₁₁ located at the end of the array ofthe series-connected group of the memory cell transistors MC₁₁ toMC_(1n). Further, a source region of the select gate transistor STD₁ forselecting the memory cell transistors MC₁₁ to MC_(1n) is connected to adrain region of the memory cell transistor MC_(1n) located at the end ofthe array of the series-connected group of the memory cell transistorsMC₁₁ to MC_(1n).

Select gate transistors STS₂ to STS_(m), memory cell transistors MC₂₁ toMC_(2n), . . . , and MC_(m1) to MC_(mn), and select gate transistorsSTD₂ to STD_(m) are also series-connected respectively, to constituteNAND strings.

A common source line SL is connected to the sources of the select gatetransistors STS₁ to STS_(m).

The memory cell transistors MC₁₁, MC₂₁, . . . , and MC_(m1), the memorycell transistors MC₁₂, MC₂₂, . . . . , and MC_(m2), . . . and the memorycell transistors MC_(1n), MC_(2n), . . . , and MC_(mn) are eachconnected by word lines WL₁ to WL_(n) which control operating voltagesto be applied to the control gate electrodes.

Further provided are a common select gate line SGS for the select gatetransistors STS₁ to STS_(m) and a common select gate line SGD for theselect gate transistors STD₁ to STD_(m).

It is to be noted that peripheral circuits, not shown, are formed on theperiphery of the memory cell array of FIG. 2.

FIG. 1 shows a cross section of a memory cell in the memory cell arrayshown in FIG. 2, e.g., the memory cell surrounded by a dashed line inFIG. 2. In the present embodiment, a case where a transistor of thememory cell is a p-type transistor having holes as carriers will bedescribed as an example.

The memory cell is formed, for example, on an n-type siliconsemiconductor layer 10 containing n-type impurities. A tunnel insulatingfilm 12 is provided on the silicon semiconductor layer 10, an organicmolecular layer 14 is provided on the tunnel insulating film 12, a blockinsulating film 16 is provided on the organic molecular layer 14, and acontrol gate electrode 18 is provided on the block insulating film 16.On both sides of the control gate electrode 18, a source region 20 and adrain region 22 are formed in the semiconductor layer 10. A region belowthe gate electrode 18 in the semiconductor layer 10 is a channel region24. The channel region 24 is interposed between the source region 20 andthe drain region 22.

Herein, the organic molecular layer 14 functions as a charge storinglayer. That is, it has a function to actively store charges as memorycell information. At the time of performing writing/erasing on thememory cell, the tunnel insulating film 12 functions as an electron/holetransfer pathway between the channel region 24 in the semiconductorlayer 10 and the organic molecular layer 14 through a tunnelingphenomenon. Further, at the time of reading/standby, the tunnelinsulating film 12 has a function to suppress electron/hole transferbetween the channel region 24 and the organic molecular layer 14 due toits barrier height. Moreover, the block insulating film 16 is aso-called interelectrode insulating film, and has a function to blockthe electron/hole flow between the organic molecular layer 14 and thecontrol gate electrode 18.

In the nonvolatile semiconductor memory device according to the presentembodiment, data is written when a positive voltage or a negativevoltage is applied to the control gate electrode 18, and data is erasedwhen a reverse voltage to that at the time of writing is applied. Whenthe positive voltage or the negative voltage is applied to the controlgate electrode 18, charges transfer in the tunnel insulating film 12 andare stored into the organic molecular layer 14, and data is thuswritten. When the reverse voltage to that at the time of writing isapplied to the control gate electrode 18, stored charges pass throughthe tunnel insulating film 12, and data is thus erased.

Other than silicon, silicon germanide, germanium, a compoundsemiconductor, and the like can be used for the semiconductor layer 10.

The tunnel insulating film 12 is, for example, an oxide film, a nitridefilm, or an oxynitride film. For example, it is a silicon oxide (SiO₂)film. The tunnel insulating film 12 may be either a single-layer film ora multilayer film. The material for the tunnel insulating film 12 is notrestricted to silicon oxide exemplified above, but another type of aninsulating film can be applied if appropriate.

The tunnel insulating film 12 desirably has a dielectric constant notlarger than 4. With the dielectric constant being not larger than 4, alater-described retention time for charges stored in the organicmolecular layer 14 is held long.

Further, a film thickness of the tunnel insulating film 12 is forexample from 1 to 10 nm, and desirably from 5 to 10 nm. When the filmthickness of the tunnel insulating film 12 is smaller than 1 nm, acharge direct tunnel phenomenon occurs between the semiconductor layer10 and the organic molecular layer 14, to shorten the retention time forcharges stored in the organic molecular layer 14.

From the viewpoint of obtaining a sufficient charge retention time, thefilm thickness is preferably not smaller than 5 nm. Further, when thefilm thickness of the tunnel insulating film 12 is larger than 10 nm,the film thickness of the entire memory cell becomes large. It is to benoted that the foregoing thicknesses are all physical film thicknesses.

When the tunnel insulating film 12 is silicon oxide, it can be formed byintroducing a silicon substrate into a thermal oxidization furnace forforcible oxidation.

The organic molecular layer 14 is made up of organic molecules and has athickness of about 1 to 20 nm, for example. The organic molecular layer14 is provided with a first organic molecular film 14 a and a secondorganic molecular film 14 b. The first organic molecular film 14 a isformed on the tunnel insulating film 12. The second organic molecularfilm 14 b is formed on the first organic molecular film 14 a.

The first organic molecular film 14 a is provided with a charge storingunit, and mainly plays, a function to store charges. The first organicmolecular film 14 a is a self-assembled monolayer (SAM).

Further, the second organic molecular film 14 b is provided withamphiphilic organic molecules. The second organic molecular film 14 b isadsorbed to the first organic molecular film 14 a. The second organicmolecular film 14 b mainly plays a function to reform the hydrophobicsurface of the first organic molecular film 14 a to the hydrophilicsurface.

The block insulating film 16 is formed on the second organic molecularfilm 14 b. The block insulating film 16 is, for example, hafnium oxide(HfO₂). Other than hafnium oxide (HfO₂) described above, for example,aluminum oxide (Al₂O₃), silicon oxide (SiO₂), zirconium oxide (ZrO₂),titanium oxide (TiO₂), and the like are used for the block insulatingfilm 16. The block insulating film 16 may be either a single-layer filmor a stacked film.

Further, a film thickness of the block insulating film 16 is for examplefrom 5 to 20 nm, and desirably from 5 to 10 nm. When the film thicknessof the block insulating film 16 is smaller than 5 nm, charges stored inthe organic molecular layer 14 quickly pass therethrough to the controlgate electrode 18 side due to the direct tunnel phenomenon, which mightshorten the charge retention time. Further, when the film thickness ofthe block insulating film 16 is not smaller than 10 nm, the total filmthickness of the nonvolatile storage device becomes large, causing animpediment to bit cost scaling. The block insulating film is, forexample, a film formed by the Atomic Layer Deposition (ALD) method.

The gate electrode 18 is, for example, polycrystalline silicon oramorphous silicon introduced with impurities and imparted withconductivity. Further, for the control gate electrode 18, metal, analloy, a metal semiconductor compound or the like may be used.

Moreover, the source region 20 and the drain region 22 are formed, forexample, of p-type diffusion layers containing p-type impurities.

FIG. 3 is an enlarged sectional view of the memory cell unit of thenonvolatile semiconductor memory device according to the presentembodiment. It is a view showing a detail of the organic molecular layer14.

The organic molecular layer 14 has a stacked or laminated structure ofthe first organic molecular film 14 a and the second organic molecularfilm 14 b. The first organic molecular film 14 a contains a plurality offirst organic molecules 26, and the second organic molecular film 14 bcontains a plurality of second organic molecules 27.

As described above, the first organic molecular film 14 a is aself-assembled monolayer (SAM).

The first organic molecule 26 has a function to store charges that areto be data of the memory cell. As shown in FIG. 3, the first organicmolecule 26 is made up of a terminal group (modified group) 26 a that ischemically bonded to the tunnel insulating film 12, a charge storingunit 26 b that stores charges, and a connecting unit 26 c that connectsbetween the terminal group 26 a and the charge storing unit 26 b.

The terminal group 26 a has a function to bond the first organicmolecules 26 onto the tunnel insulating film 12 through a chemical bond(covalent bond, ionic bond, or metallic bond). Thereby, the firstorganic molecules 26 are arranged on the tunnel insulating film 12without being a multilayer. For this reason, the first organic molecules26 compose a monomolecular film, and it is thus possible to ensure theuniformity of the film thickness and achieve scaling-down of the deviceby decreasing the film thickness.

For the terminal group 26 a, it is desirable to use a chemical reactiongroup which is generally used for the self-assembled monolayer (SAM).For example, one for the terminal group 26 a is desirably selected froma silyl group, an alkoxysilyl group, an alkylsilyl group, a chlorosilylgroup, a phosphoryl group, an alkyl selenide group, a telluride group, asulfide group, a disulfide group, a thio group, an isocyanate group, analkyl bromide group, a carbonyl group, an alkoxy group, alkane andalkene.

Further, when a metal oxide is used for the tunnel insulating film 12,the terminal group 26 a is desirably a group showing a chemicalreactivity to the metal oxide. Examples of the group showing a chemicalreactivity to the metal oxide include a hydroxy group, a methoxysilylgroup, a trimethoxysilyl group, a dimethyl-methoxysilyl group, adiethyl-methoxysilyl group, an ethoxysilyl group, a triethoxysilylgroup, a dimethyl-ethoxysilyl group, a diethyl-ethoxysilyl group, athiol group, a carboxyl group, a sulfone group, and a phosphonate group.From the viewpoints of ease of organic synthesis and the chemicalreactivity with metal oxide, it is preferable to use the methoxysilylgroup, the trimethoxysilyl group, the ethoxysilyl group, thedimethyl-ethoxysilyl group, the triethoxysilyl group, and thephosphonate group. Further, when the metal oxide is aluminum oxide(Al₂O₃), the phosphonate group is preferably used.

The charge storing unit 26 b has a function to store charges byapplication of an electric field. The charge storing unit 26 bpreferably has a multicyclic structure. It is, for example, possible toapply macrocyclic molecules represented by porphyrin and phthalocyanine,and non-macrocyclic molecules such as metallocene, pentacene,anthracene, oligophenylenevinylene, thiophene, tetrathiafulvalene,tetracyanoquinodimethane, tetramethyltetraselenafulvalene, andfullerene. These molecules are not restrictive, but derivatives of thoseare also applicable.

The charge storing unit 26 b is preferably a porphyrin derivative, aphthalocyanine derivative, a chlorine derivative, a tetrapyrrolederivative, a bipyridine derivative, an indole derivative, an acenederivative, a quinoxaline derivative, a phenylenevinylene derivative, ora fullerene derivative.

The charge storing unit 26 b is desirably organic molecules having amulticyclic structure with a molecular weight of not smaller than 100and not larger than 2000. When the molecular weight falls below 100, thedevelopment of a sufficient n-conjugated system cannot be obtained, thusmaking it difficult to achieve a stable charge exchange(oxidation-reduction reaction). When the molecular weight exceeds 2000,the thickness as the charge storing layer increases, thus making itdifficult to meet the requirement for scaling-down.

FIGS. 4A to 4D are diagrams each exemplifying a molecular structure of acharge storing unit according to the first embodiment. These areexamples of porphyrin, the porphyrin derivative, phthalocyanine, and thephthalocyanine derivative which are preferable for the charge storingunit 26 b.

Examples of R1 to R3 and R of FIGS. 4A to 4D include hydrogen, an alkylgroup, a fluoroalkyl group, an alkoxy group, an aryl group, a halogengroup, a hydroxy group, an amino group, a nitro group, a phenyl group, acycloalkyl group, a carboxy group, an amide group, an imide group, acyano group, a thiol group, and a fluorophenyl group, provided that atleast one is bonded to the connecting unit 26 c. In this case, astructure such as an ether bond (—O—) or an amino bond (—NH—), inaddition to a C—C bond, may be introduced between the charge storingunit 26 b and the connecting unit 26 c.

When a central metal (ME) is contained as in FIG. 4B, charge exchangewith an electron orbit of the metal may occur. A metal element in thiscase is selected, for example, from Zn (zinc), Ti (titanium), Cu(copper), Ir (iridium), Ru (ruthenium), Ni (nickel), Co (cobalt), Li(lithium), Mn (manganese), and Mg (magnesium). Further, when an-conjugated system is formable, a macrocyclic molecular structurecontaining hetero atoms, as those shown in FIGS. 4B and 4D, ispreferable.

FIGS. 5 and 6 are diagrams exemplifying molecular structures of thecharge storing unit 26 b. FIG. 5 shows a metallocene derivative, andFIG. 6 shows a fullerene derivative.

X in FIG. 5 is a group connecting the charge storing unit 26 b and thetunnel insulating film 12, and corresponds to the terminal group 26 a inFIG. 3 or corresponds to the terminal group 26 a and the connecting unit26 c.

Further, X in FIG. 6 is a group connecting the charge storing unit 26 band the tunnel insulating film 12, and corresponds to the terminal group26 a in FIG. 3 or corresponds to the terminal group 26 a and theconnecting unit 26 c.

The connecting unit 26 c plays a function to connect the terminal group26 a and the charge storing unit 26 b. Examples thereof includesaturated alkyl chains such as an alkyl chain, a phenyl chain, amethylene chain, an ethylene chain, a trimethylene chain, atetramethylene chain, a pentamethylene chain, a hexamethylene chain, aheptamethylene chain, an octamethylene chain, a nonamethylene chain anda decamethylene chain, as well as a phenylene chain, a biphenylenechain, and a terphenylene chain

Using the length of the alkyl chain or the phenylene chain to serve asthe connecting unit 26 c, it is possible to control the distance betweenthe insulating layer and the charges which are stored in the chargestoring unit 26 b. As the chain length is longer, the tunnel distance ofthe charges increases and thus the charge retention time increases. Onthe other hand, when the chain length is excessively long, the size ofthe molecule increases, thereby making a total film thickness of thecapacitor large. For this reason, in the case of the saturated alkyl,the chain length is desirably about 5 to 15 carbons.

The second organic molecule 27 is the amphiphilic organic molecule. Theamphiphilic organic molecule is a module having chemical structures ofboth hydrophobic (lipophilic) properties and hydrophilic properties. Inother words, it is a molecule containing therewithin both a hydrophobic(lipophilic) group and a hydrophilic group.

The second organic molecule 27 is provided with a hydrophobic unit 27 acontaining a hydrophobic group (lipophilic group), and a hydrophilicunit 27 b containing a hydrophilic group. The second organic molecule 27has a function to render the surface of the organic molecular layer 14hydrophilic.

It is to be noted that in the present specification, the “amphiphilicorganic molecule” includes a structure derived from the amphiphilicorganic molecule. Herein, the structure derived from the amphiphilicorganic molecule means a structure where the amphiphilic organicmolecules at the time of film formation are, for example, bonded toatoms constituting an upper layer film such as the block insulating film16 and the amphiphilic organic molecule are thereby bonded to the upperlayer film.

The first organic molecular film 14 a as the self-assembled monolayer islikely to be the hydrophobic surface. For this reason, when the blockinsulating film 16 made up of metal oxide is intended to be formed onthe first organic molecular film 14 a by ALD (Atomic Layer Deposition),only a low-density, highly defective block insulating film 16 may beobtained. This is because, with the surface energy of the first organicmolecular film 14 a being low and the surface energy of the blockinsulating film 16 being high, there is a large difference in surfaceenergy therebetween, making it difficult to form the block insulatingfilm 16.

In the present embodiment, the second organic molecular film 14 bcontaining the amphiphilic organic molecules is provided between theblock insulating film 16 and the first organic molecular film 14 a. Thesecond organic molecular film 14 b leads to an increase in the surfaceenergy of the first organic molecular film 14 a, namely the surfaceenergy of the organic molecular layer 14.

The amphiphilic organic molecule 27 is required to be easily adsorbedonto the surface of the first organic molecular film 14 a. Further, theamphiphilic organic molecules 27 are required to render the secondorganic molecular film 14 b after adsorption being hydrophilic. That is,the amphiphilic organic molecules 27 are required to increase thesurface energy of the second organic molecular film 14 b.

The hydrophobic unit 27 a of the amphiphilic organic molecule 27 rendersthe amphiphilic organic molecule 27 being more easily adsorbed onto thesurface of the first organic molecular film 14 a. Further, thehydrophilic units 27 b of the amphiphilic organic molecules 27 increasethe surface energy of the second organic molecular film 14 b after theadsorption, that is, render the surface being hydrophilic.

Examples of the chemical structure of the hydrophobic unit 27 a includemolecular structures made up only of an alkyl chain, a fluoroalkylgroup, a polysilane chain, a phenylene chain, or the like without anyhydrophilic groups such as an ether group, a carboxy group, a hydroxygroup, an amino group and a thiol group. In the molecular structure, amain chain may be branched.

From the viewpoint of productivity, desirable molecular structures ofthe hydrophobic unit 27 a are ones showing strong hydrophobic propertiessuch as the alkyl chain and the polysilane chain. This is because theamphiphilic organic molecule 27 shows an affinity with the first organicmolecular film 14 a with strong hydrophobic properties and thus tends tobe physically adsorbed onto it.

Examples of the chemical structure of the hydrophilic unit 27 b includealcohol, calboxylic acid, amine, ethylene and ethylene glycol containingthe ether group, the hydroxy group, the amino group, the thiol group, orthe like. From the viewpoint of productivity, ethylene glycol isdesirable.

Considering the above chemical structure, the amphiphilic organicmolecule 27 is desirably a surfactant. Although examples of thesurfactants may include ionic surfactants such as monoalkyl sulfate andakyltrimethylammonium salt, the ionic surfactant tends to becomeimpurities which change a concentration of carriers of the semiconductorsubstrate, and is thus not preferable. For this reason, the amphiphilicorganic molecule 27 is desirably a nonionic surfactant.

Examples of the nonionic surfactants include an esterified foodemulsifier, glycerin-fatty acid ester used for an emulsion stabilizer, asorbitan fatty acid ester used for a food additive, sucrose fatty acidester, etherified alkyl polyethylene glycol, polyoxyethylene phenylether, and alkylglycoside. From the viewpoint of productivity, alkylpolyethylene glycol is desirable.

The second organic molecules 27 is, for example, polyethylene glycolalkylether shown in General Formula (I) below.

Further, the second organic molecules 27 is, for example,trisiloxanepolyethylene glycol shown in General Formula (II).

In the General Formulas (I) and (II), n and m are integers representinglengths of molecular chains. When the molecular chain is excessivelyshort, the molecular weight becomes small, and thermal decompositionthus is likely to occur, which is not preferable. On the other hand,when the molecular chain is excessively long, a voluminal proportion ofthe molecules increases, and a film thickness thus becomes large, whichis not preferable. Hence n and m in General Formula (I) and (II) aredesirably integers not smaller than 3 and not larger than 20.

FIG. 7 is a diagram exemplifying a molecular structure of the secondorganic molecules 27. FIG. 7 shows pentaethyleneglycol monododecylether.Pentaethyleneglycol monododecylether is desirable since it can besynthesized at low cost.

FIGS. 8 and 9 are structural diagrams of the organic molecular layer 14.As shown in FIG. 8, a stacked structure may be formed in the organicmolecular layer 14 where a boundary (dashed line in FIG. 8) between thefirst organic molecular film 14 a and the second organic molecular film14 b is a substantially plane. Further, as shown in FIG. 9, a mixedstructure may be formed where a boundary (dashed line in FIG. 9) betweenthe first organic molecular film 14 a and the second organic molecularfilm 14 b is an irregular plane. Since the second organic molecules 27is adsorbed to the periphery of the first organic molecules 26 by anintermolecular mutual function, when a density of the first organicmolecules 26 occupying the first organic molecular film 14 a is low, thesecond organic molecules 27 enter thereinto to form a mixed structure.

The first organic molecular film 14 a made up of the first organicmolecules 26 and the second organic molecular film 14 b made up of thesecond organic molecules 27 can be detected by the following analysismethods. That is, the first organic molecule 26 and the second organicmolecule 27 can be detected using a mass spectroscope (MS), a secondaryionic mass spectrometer (SIMS), a nuclear magnetic resonator (NMR), anelement analyzer, an infrared reflection absorption spectroscopy(IR-RAS), an X-ray fluorescence instrument (XRF), an X-ray photoelectroninstrument (XPS), an ultraviolet-visible spectrophotometer (UV-vis), aspectrophotofluorometer (FL), or the like.

When an insulating film of metal oxide or the like is formed on thefirst organic molecular film 14 a made up of the first organic molecules26 and the second organic molecular film 14 b made up of the secondorganic molecules 27, for example, the analysis is performed whileshaving the surface, for example, with a sputter using argon ions, orthe like. Alternatively, the first organic molecular film 14 a made upof the first organic molecules 26 and the second organic molecular film14 b made up of the second organic molecules 27 are dissolved and peeledby a hydrofluoric acid aqueous solution or the like, simultaneously withthe insulating layer of the metal oxide or the like, and the solution isanalyzed.

Further, in the method for performing the analysis by shaving thesurface by means of the above sputter or the like, heating processingmay be performed as the shaving method. In this case, a gas containingthe shaved material may be adsorbed to another material such as anactivated carbon, and another material such as the activated carbonadsorbed with the gas may be analyzed and detected. Further, in themethod for peeling the material by the hydrofluoric acid aqueoussolution or the like and analyzing the solution, the dissolved andpeeled material may be subjected to a reduced pressure or a thermaltreatment to be concentrated, and may then be analyzed and detected.

Next, a method for manufacturing the nonvolatile semiconductor memorydevice according to the present embodiment will be described withreference to FIGS. 1 and 3.

The method for manufacturing the nonvolatile semiconductor deviceaccording to the present embodiment includes: forming the tunnelinsulating film 12 on the semiconductor layer 10; forming on the tunnelinsulating film 12 the first organic molecular film 14 a that containsthe first organic molecules 26 having the charge storing unit 26 b as amonomolecular film by self-assembling; forming on the first organicmolecular film 14 a the second organic molecular film 14 b that containsthe second organic molecules 27 as amphiphilic organic molecules;forming the block insulating film 16 on the second organic molecularfilm 14 b; and forming the control gate electrode 18 on the blockinsulating film 16.

For example, the tunnel insulating film 12 is formed on thesemiconductor layer (semiconductor substrate) 10 of monocrystallinesilicon. When the tunnel insulating film 12 is silicon oxide, it can beformed, for example, by introducing a silicon substrate into a thermaloxidization furnace for forcible oxidation.

Further, it is also possible to form it by means of Atomic LayerDeposition (ALD) or a film forming device such as a sputter. In the caseof film formation, it is desirable to anneal the insulating film afterthe film formation, by means of a Rapid Thermal Annealing (RTA) device.

Thus, the organic molecular layer 14 is formed on the tunnel insulatingfilm 12. First, the first organic molecular film 14 a is formed byself-assembling, and the second organic molecular film 14 b issubsequently formed on the first organic molecular film 14 a.

In the case of forming the first organic molecular film 14 a by theself-assembling, for example, the following soaking method isapplicable.

The surface of the tunnel insulating film 12 to serve as a foundationwhere the first organic molecules 26 are introduced is cleaned. For thiscleaning, it is possible to employ, for example, cleaning by means of amixed solution of sulfuric acid and hydrogen peroxide solution (a mixedratio is 2:1, for example), or a UV cleaning performed by irradiatingthe insulating film surface with ultraviolet light.

Next, the surface of the tunnel insulating film 12 is soaked in asolution obtained by dissolving the first organic molecules 26 in asolvent, and the terminal group 26 a showing chemical reactivity to thetunnel insulating film 12 is brought into reaction with the surface ofthe tunnel insulating film 12. It can be considered to use a solvent inwhich the first organic molecule 26 is easily dissolved.

As the solvent, organic solvents such as acetone, toluene, ethanol,methanol, hexane, cyclohexanone, isopropyl alcohol, benzene,chlorobenzene, toluene, xylene, tetrahydrofuran, dimethylsulfoxide,N,N-dimethylformamide, anisole, cyclohexanone, and methoxypropionic acidmethyl may be included. In the case where the first organic molecules 26can be dissolved in water, it is possible to use water as the solvent.

Regarding the concentration of the first organic molecules 26 to bedissolved in the solvent, when it is excessively low, the reaction timebecomes longer, and when it is excessively high, unnecessary adsorptionmolecules that need to be removed by a rinsing operation increase. Hencethe concentration is desirably set to be an appropriate one. Forexample, the concentration of the organic material is desirably set toabout 1 to 100 mM.

Further, at this time, a catalyst may be added for the purpose ofincreasing the reactivity between the cleaned surface of the tunnelinsulating film 12 and the first organic molecule 26. As the catalyst,acetic acid, formic acid, propionic acid, trifluoroacetic acid,triethylamine and ammonia which can be dissolved in the solvent areused. The amount of the catalyst added is desirably small, since theorganic material is self-reacted in the solvent causing a side reactionsuch as polymerization when it is excessively large. It is desirably notlarger than 3% with respect to a volume of the solution.

The time for soaking the surface of the tunnel insulating film 12 in thesolution dissolved with the organic material is desirably the extent ofthe time for occurrence of a sufficient reaction, and specifically, itis desirably not shorter than one minute. The surface is then soaked inthe used solvent, and rinsed using an ultrasonic cleaner. Since theunnecessarily physically adsorbed organic molecules are rinsed in thisoperation, it is desirable to at least replace the solvent by a new oneand repeat the operation twice or more.

Subsequently, the surface is soaked in ethanol, and rinsed by use of theultrasonic cleaner. This leads to formation of a monomolecular film madeof the first organic molecules 26, namely the first organic molecularfilm 14 a.

Next, the second organic molecular film 14 b is formed on the firstorganic molecular film 14 a. For forming the second organic molecularfilm 14 b, for example, the following soaking method can be applied.

The semiconductor substrate 10 whose surface is the first organicmolecular film 14 a is dissolved in a solution obtained by dissolvingthe second organic molecules 27 in the solvent, and the second organicmolecules 27 are adsorbed to the first organic molecular film 14 a. Asthe solvent, it is considered to use one in which the second organicmolecule 27 tends to be dissolved.

As the solvent, organic solvents such as acetone, toluene, ethanol,methanol, hexane, cyclohexanone, isopropyl alcohol, benzene,chlorobenzene, toluene, xylene, tetrahydrofuran, dimethylsulfoxide,N,N-dimethylformamide, anisole, cyclohexanone, and methoxypropionic acidmethyl may be included. In the case where the second organic molecule 27can be dissolved in water, it is possible to use water as the solvent.

Regarding the concentration of the second organic molecules to bedissolved in the solvent, when it is excessively low, the adsorptiontime becomes longer, and when it is excessively high, unnecessarymultilayer adsorption molecules that need removing by the rinsingoperation increase. Hence the concentration is desirably set to be anappropriate one. For example, the concentration of the second organicmolecules is desirably set to about 1 to 100 mM.

The time for soaking the semiconductor substrate 10 in the solutiondissolved with the second organic molecules 27 is desirably the extentof the time for occurrence of sufficient reaction, and specifically, itis desirably not shorter than one minute. It is then soaked to rinse inthe used solvent. It is to be noted that, although an ultrasonic cleanermay be used in the rinsing operation, it is better to complete thetreatment within a minute since the adsorbed second organic molecules 27are completely desorbed if the operation is performed for a long periodof time.

In addition, at the time of forming the second organic molecular film 14b, the following spin-coating method may be applied.

In this case, the semiconductor substrate 10 formed with the firstorganic molecular film 14 a on its surface is fixed to a stage of a spincoater. The solution obtained by dissolving the second organic molecules27 in the solvent is then spin-coated.

The solvent used for the solution of the second organic molecules 27which is spin-coated is desirably the same one as is used in the abovesoaking method. As for a concentration of the solution, when it isexcessively high, an unnecessary, multilayer and physically adsorbeddeposit increases, and when it is excessively low, a sufficientadsorption amount of second organic molecules 27 cannot be obtained. Forthis reason, as in the above soaking method, the concentration isdesirably set to about 1 to 100 mM.

After the application, the semiconductor substrate 10 may be heated on ahot plate, to evaporate the solvent used for the solution of the secondorganic molecule 27. The temperature of the hot plate is desirably atemperature at which the solvent used for the solution of the secondorganic molecules 27 tends to evaporate and the second organic molecules27 resist reaction with impurities in the air. That is, it is desirablyabout 100 to 150° C. It is also desirable that the heating time has alength in which the solvent used for the solution of the second organicmolecules 27 tends to evaporate and the second organic molecules 27resist reaction with impurities in the air. That is, it is desirablyabout 30 to 120 seconds.

Using the above method, the organic molecular layer 14 is formed wherethe second organic molecular film 14 b is adsorbed onto the firstorganic molecular film 14 a.

Thereafter, for example, a hafnium oxide film is deposited on theorganic molecular layer 14 by ALD (Atomic Layer Deposition), to form theblock insulating film 16.

The block insulating film 16 can be formed by using ALD (Atomic LayerDeposition), spin-coating, sputtering, or the like. A formation methodwhere the organic molecular layer 14 formed of the organic molecules isnot disassembled and a damage is small is desirable. For example,thermal ALD or spin-coating is desirable. It is desirable that theinsulating film after the film formation is annealed using a RapidThermal Annealing (RTA) device, since an atomic density in the filmincreases.

An impurity-doped polycrystalline silicon film is then formed by CVD(Chemical Vapor Deposition), for example, to form the control gateelectrode 18. The stacked films are then patterned, thereby to form agate electrode structure.

Subsequently, for example, p-type impurities are ion-planted using thecontrol gate electrode 18 as a mask, to form the source region 20 andthe drain region 22. In such a manner, it is possible to manufacture thenonvolatile semiconductor memory device shown in FIG. 1.

In the case of forming a film of the first organic molecules 26 which isprovided with the charge storing unit 26 b by self-assembling to form itas the first organic molecular film 14 a being the self-assembledmonolayer, the first organic molecular film 14 a tends to be ahydrophobic surface. For example, when a metal oxide film is intended tobe formed on the hydrophobic surface, initial film formation reaction isdifficult to occur, and a film with inferior quality might be formed.That is, a film having inferior insulation properties and a lowreliability might be formed.

According to the present embodiment, the second organic molecular film14 b formed of the second organic molecules 27 as the amphiphilicorganic molecules are formed on the first organic molecular film 14 a.This can render the surface of the organic molecular layer 14 beinghydrophilic. Hence it is possible to improve a quality of the filmformed on the organic molecular layer 14.

For example, in the case of forming a film of aluminum oxide as themetal oxide by ALD, the substrate is exposed alternately to water andtrimethylaluminium while heated, to form the aluminum oxide film.However, when the substrate surface is hydrophobic, it tends to repelwater and trimethylaluminium rejects reaction with the surface, wherebythe aluminum oxide film tends to be a low-density film.

Nevertheless, when the second organic molecules 27 as the amphiphilicorganic molecules are introduced thereinto to render the substratesurface being hydrophilic, water wettability is better andtrimethylaluminium is likely to react with the surface. For this reason,a high-density aluminum oxide film is formed. When another metal oxideis to be formed, for a similar reason, a high-density film is obtainedby introducing the second organic molecules 27.

According to the present embodiment, therefore, it is possible torealize the block insulating film 16 with high quality. This leads to animprovement in insulation properties between the charge storing unit 26b and the control gate electrode 18. It is thus possible to realize thenonvolatile semiconductor memory device excellent in data retentionproperties. Further, the reliability in block insulating film improves,to allow realization of the nonvolatile semiconductor memory deviceexcellent in reliability.

Moreover, the block insulating film 16 can be made thinner while holdinginsulation properties. Hence it is possible to realize the nonvolatilesemiconductor device provided with the fine memory cell.

Second Embodiment

A nonvolatile semiconductor memory device according to this embodimentdiffers from that of the first embodiment in that the tunnel insulatingfilm is not provided and the first organic molecular film in the organicmolecular layer has a function of the tunnel insulating film.Hereinafter, descriptions of contents that overlap with those of thefirst embodiment will be omitted.

FIG. 10 is a sectional view of a memory cell unit of the nonvolatilesemiconductor memory device according to the present embodiment.

The memory cell is formed, for example, on an n-type siliconsemiconductor layer 10 containing n-type impurities. The organicmolecular layer 14 is provided on the semiconductor layer 10, the blockinsulating film 16 is provided on the organic molecular layer 14, andthe control gate electrode 18 is provided on the block insulating film16. On both sides of the control gate electrode 18, the source region 20and the drain region 22 are formed in the semiconductor layer 10. Aregion below the gate electrode 18 in the semiconductor layer 10 is thechannel region 24. The channel region 24 is interposed between thesource region 20 and the drain region 22.

The first organic molecular film 14 a in the organic molecular layer 14also has the function of the tunnel insulating film.

In the present embodiment, the first organic molecules 26 contained inthe first organic molecular film 14 a are chemically bonded directly tothe semiconductor layer 10. Then, the first organic molecular film 14 ais a self-assembled monolayer.

As in the first embodiment, the first organic molecule 26 has a functionto store charges that are to be data of the memory cell. As shown inFIG. 3, the first organic molecule 26 is made up of a terminal group(modified group) 26 a that is chemically bonded to the tunnel insulatingfilm 12, a charge storing unit 26 b that stores charges, and aconnecting unit 26 c that connects the terminal group 26 a and thecharge storing unit 26 b.

Then, the first organic molecule 26 is provided with an insulating unitbetween the charge storing unit 26 b and the semiconductor layer 10.Herein, the connecting unit 26 c corresponds to the insulating unit. Theconnecting unit 26 c contains straight chain saturated hydrocarbon.

The connecting unit 26 c is, for example, an alkyl molecular chain. Thealkyl molecular chain is, for example, an alkyl chain, an isoalkyl chainor a halogen alkyl chain. The connecting unit 26 c may be provided witha side chain. The function as the tunnel insulating film is exerted bythis alkyl molecular chain.

For this reason, the carbon number of the alkyl molecular chain ispreferably not smaller than 8 and not larger than 30, and is moredesirably not smaller than 10 and not larger than 20. This is because,when the carbon number is below the above range, the insulatingresistance might deteriorate and the self-assembled monolayer might bedifficult to form. Further, when the carbon number exceeds the aboverange, the film thickness might be large, rendering the scaling-downbeing difficult. Especially, the carbon number of the alkyl molecularchain is further desirably 18 since the self-assembled monolayer canthen be manufactured in a stable manner.

Moreover, since a dielectric constant of the alkyl molecular chain isabout 2 to 3 which is higher than that of vacuum, the electric fieldapplied to the insulating region is small as compared with that ofvacuum. For this reason, the FN (Fowler-Nordheim) tunneling probabilityis also is low, as compared with that in vacuum. Hence, as a density ofthe alkyl molecular chain increases and a gap (vacuum unit) between thealkyl molecular chains becomes smaller, the insulation resistanceimproves. Also from this viewpoint, it is desirable to form the alkylmolecular chain as the self-assembled monolayer.

Further, the alkyl molecular chain also has an advantage of facilitatingthe formation of a high-density film since its intermolecular force, inparticular, stably functions among self-assemblable molecules.

The method for manufacturing the nonvolatile semiconductor deviceaccording to the present embodiment includes: forming on thesemiconductor layer 10 the first organic molecular film 14 a thatcontains the first organic molecules 26 having the charge storing unit26 b as a monomolecular film by self-assembling; forming on the firstorganic molecular film 14 a the second organic molecular film 14 b thatcontains the second organic molecules 27 as amphiphilic organicmolecules; forming the block insulating film 16 on the second organicmolecular film 14 b; and forming the control gate electrode 18 on theblock insulating film 16.

For example, the organic molecular layer 14 is formed on thesemiconductor layer (semiconductor substrate) 10 of monocrystallinesilicon. The first organic molecular film 14 a is formed byself-assembling, and the second organic molecular film 14 b issubsequently formed on the first organic molecular film 14 a.

The above is similar to that in the first embodiment except that theorganic molecular layer 14 is formed directly on the semiconductor layer10.

According to the above embodiment, in place of the tunnel insulatingfilm of an inorganic material such as an oxide, the first organicmolecular film 14 a realizes the function of the tunnel insulating film,thereby to allow a reduction in physical thickness of the memory cellstructure. Hence it is possible to realize the nonvolatile semiconductordevice provided with the fine memory cell.

Further, eliminating the need for formation of the tunnel insulatingfilm of the inorganic material can realize simplification of themanufacturing process.

Third Embodiment

A nonvolatile semiconductor memory device according to the presentembodiment is similar to in the first embodiment except that aconductive layer is formed between the semiconductor layer and theorganic molecular layer. Hereinafter, descriptions of contents thatoverlap with those of the first embodiment will be omitted.

FIG. 11 is a sectional view of a memory cell unit of the nonvolatilesemiconductor memory device according to the present embodiment.

The memory cell is formed, for example, on an n-type siliconsemiconductor layer 10 containing n-type impurities. The tunnelinsulating film 12 is provided on the silicon semiconductor layer 10, aconductive layer 30 is provided on the tunnel insulating film 12, theorganic molecular layer 14 is provided on the conductive layer 30, theblock insulating film 16 is provided on the organic molecular layer 14,and the control gate electrode 18 is provided on the block insulatingfilm 16. On both sides of the control gate electrode 18, the sourceregion 20 and the drain region 22 are formed in the semiconductor layer10. A region below the gate electrode 18 in the semiconductor layer 10is a channel region 24. The channel region 24 is interposed between thesource region 20 and the drain region 22.

The conductive layer 30 has a function to uniformly disperse chargesstored in the organic molecular layer 14. Accordingly, a constantconcentration distribution of charges without variations is realizedinside the organic molecular layer 14, to realize a stable operation.Further, the conductive layer 30 has a function to read charges storedin the organic molecular layer 14 so as to improve writing efficiency.

The conductive layer 30 is, for example, a semiconductor film, a metalfilm, or a metal compound film. For example, it is possible to usepolycrystalline silicon or amorphous silicon introduced with impuritiesto impart conductivity.

In the case of the present embodiment, the first organic molecule 26 isbonded onto the conductive layer 30 by self-assembling. In this case,when the conductive layer 30 is silicon, the terminal group 26 a of thefirst organic molecule 26 is desirably a thiol group from the viewpointof facilitating the bonding.

The method for manufacturing the nonvolatile semiconductor deviceaccording to the present embodiment includes: forming the tunnelinsulating film 12 on the semiconductor layer 10; forming the conductivelayer 30 on the tunnel insulating film 12; forming on the conductivelayer 30 the first organic molecular film 14 a that contains the firstorganic molecules 26 having the charge storing unit 26 b as amonomolecular film by self-assembling; forming on the first organicmolecular film 14 a the second organic molecular film 14 b that containsthe second organic molecules 27 as amphiphilic organic molecules;forming the block insulating film 16 on the second organic molecularfilm 14 b; and forming the control gate electrode 18 on the blockinsulating film 16.

The conductive layer 30 is formed on the tunnel insulating film 12 forexample, by CVD, ALD or sputtering. The organic molecular layer 14 isthen formed on the conductive layer 30.

The above is similar to that in the first embodiment except that thetunnel insulating film 12 is formed on the semiconductor layer 10 andthe organic molecular layer 14 is formed on the conductive layer 30.

According to the present embodiment, it is possible to realize anonvolatile semiconductor memory device whose operation is stable and isexcellent in reading and writing characteristics.

Fourth Embodiment

A nonvolatile semiconductor memory device according to an embodimentincludes: a semiconductor layer; a control gate electrode; and anorganic molecular layer, which is formed between the semiconductor layerand the block insulating film, and provided with a first organicmolecular film containing first organic molecules on the semiconductorlayer side and a second organic molecular film containing second organicmolecules on the block insulating film side, and in which the firstorganic molecule has a charge storing unit and the second organicmolecule is an amphiphilic organic molecule. A nonvolatile semiconductormemory device according to this embodiment differs from that of thesecond embodiment in that the block insulating film is not provided andthe second organic molecular film in the organic molecular layer has afunction of the block insulating film. Hereinafter, descriptions ofcontents that overlap with those of the second embodiment will beomitted.

FIG. 12 is a sectional view of a memory cell unit of the nonvolatilesemiconductor memory device according to the present embodiment.

The memory cell is formed, for example, on an n-type siliconsemiconductor layer 10 containing n-type impurities. The organicmolecular layer 14 is provided on the semiconductor layer 10, and thecontrol gate electrode 18 is provided on the organic molecular layer 14.On both sides of the control gate electrode 18, the source region 20 andthe drain region 22 are formed in the semiconductor layer 10. A regionbelow the gate electrode 18 in the semiconductor layer 10 is a channelregion 24. The channel region 24 is interposed between the source region20 and the drain region 22.

As in the second embodiment, the first organic molecular film 14 a inthe organic molecular layer 14 also has the function of the tunnelinsulating film. Further, the second organic molecular film 14 b in theorganic molecular layer 14 also has the function of the block insulatingfilm.

The second organic molecule 27 contained in the second organic molecularfilm 14 b contains straight chain saturated hydrocarbon. Straight chainsaturated hydrocarbon leads to an improvement in insulation properties.

It is to be noted that saturated hydrocarbon may contain oxygen in itsstructure. For example, even ethylene glycol is applicable when itsmolecular chain is long. Further, polysilane is known to haveconductivity, and is thus not desirable.

The length of the molecular chain is desirably not smaller than 1 nm,and more desirably not smaller than 2 nm.

A main chain of the second organic molecule 27 is, for example, an alkylmolecular chain. The alkyl molecular chain is, for example, an alkylchain, an isoalkyl chain or a halogen alkyl chain. The second organicmolecule 27 may be a molecule provided with a side chain.

For this reason, the carbon number of the alkyl molecular chain ispreferably not smaller than 8 and not larger than 30, and is moredesirably not smaller than 10 and not larger than 20. This is because,when the carbon number falls below the above range, the insulationproperties might deteriorate. Further, when the carbon number exceedsthe above range, the film thickness might become large, to render thescaling-down being difficult.

As a material for the control gate electrode 18, there is used aconductive material which can obtain favorite film characteristic whenforming a foundation for the hydrophilic surface to, e.g., metals suchas nickel (Ni) and titanium (Ti).

The method for manufacturing the nonvolatile semiconductor deviceaccording to the present embodiment includes: forming on thesemiconductor layer 10 the first organic molecular film 14 a thatcontains the first organic molecules 26 having the charge storing unit26 b as a monomolecular film by self-assembling; forming on the firstorganic molecular film 14 a the second organic molecular film 14 b thatcontains the second organic molecules 27 as amphiphilic organicmolecules; and forming the control gate electrode 18 on the secondorganic molecular film 14 b.

For example, the organic molecular layer 14 is formed on thesemiconductor layer (semiconductor substrate) 10 of monocrystallinesilicon. The first organic molecular film 14 a is formed byself-assembling, and the second organic molecular film 14 b issubsequently formed on the first organic molecular film 14 a.

Then, the control gate electrode 18 is formed on the second organicmolecular film 14 b, for example, by CVD, ALD or the like.

The above is similar to that in the first embodiment except that theorganic molecular layer 14 is formed directly on the semiconductor layer10, and the control gate electrode 18 is formed directly on the organicmolecular layer 14.

According to the present embodiment, the organic molecular layer 14 ismade to play both functions of the tunnel insulating film and the blockinsulating film. Therefore, the physical film thickness of the memorycell structure can be small. Hence it is possible to realize thenonvolatile semiconductor device provided with the fine memory cell.

Further, eliminating the need for the formation of the tunnel insulatingfilm of the inorganic material and the block insulating film can realizesimplification of the manufacturing process.

Fifth Embodiment

A nonvolatile semiconductor memory device according to the presentembodiment is similar to that in the first embodiment except that atransistor of the memory cell is an n-type transistor whose carriers areelectrons. Hence descriptions of contents that overlap with those of thefirst embodiment will be omitted.

FIG. 13 is a sectional view of a memory cell unit of the nonvolatilesemiconductor memory device according to the present embodiment.

The memory cell is formed, for example, on a p-type siliconsemiconductor layer 10 containing p-type impurities. The tunnelinsulating film 12 is provided on the silicon semiconductor layer 10,the organic molecular layer 14 is provided on the tunnel insulating film12, the block insulating film 16 is provided on the organic molecularlayer 14, and the control gate electrode 18 is provided on the blockinsulating film 16. On both sides of the control gate electrode 18, thesource region 20 and the drain region 22 are formed in the semiconductorlayer 10. A region below the gate electrode 18 in the semiconductorlayer 10 is a channel region. The channel region 24 is interposedbetween the source region 20 and the drain region 22.

Moreover, the source region 20 and the drain region 22 are formed, forexample, of n-type diffusion layers containing n-type impurities.

A charge storing unit 26 b of the first organic molecule 26 in theorganic molecular layer 14 is applied with molecules that storeelectrons as charges. For example, fullerene shown in FIG. 7 can beused.

Similarly to the first embodiment, also in the present embodiment, usingthe amphiphilic organic molecules as the second organic molecules 27 inthe organic molecular layer 14 allows realization of the nonvolatilesemiconductor device provided with a fine memory cell excellent in datastoring characteristics and reliability.

Sixth Embodiment

A nonvolatile semiconductor memory device according to the presentembodiment includes: a stacked structure in which insulating layers andcontrol gate electrode layers are alternately stacked; a blockinsulating film provided on the side surface of a hole that is providedpenetrating the stacked structure from its top surface to the lowermostcontrol gate electrode layer with respect to a stacking direction of thestacked structure; an organic molecular layer, which is provided with afirst organic molecular film containing the first organic molecules andformed on the inner surface of the block insulating film, and a secondorganic molecular film containing second organic molecules and formed onthe inner surface of the first organic molecular film, and in which thefirst organic molecule has a charge storing unit and the second organicmolecule is an amphiphilic organic molecule; a tunnel insulating filmprovided on the inner surface of the organic molecular layer; and asemiconductor layer provided on the inner surface of the tunnelinsulating film.

The nonvolatile semiconductor memory device according to the presentembodiment differs from that of the first embodiment in that it is athree-dimensional device using the so-called BiCS (Bit-Cost Scalable)technique. As for the organic molecular layer, however, it is similar toin the first embodiment except that the first organic molecular film isprovided on the block insulating film side and the second organicmolecular film is provided on the tunnel insulating film side. Hencedescriptions of contents that overlap with those of the first embodimentwill be omitted.

FIG. 14 is a three-dimensional conceptual diagram of the nonvolatilesemiconductor memory device according to the present embodiment. FIG. 15is an X-Y sectional view of FIG. 14. FIG. 16 is an X-Z sectional view ofFIG. 14.

The nonvolatile semiconductor memory device according to the presentembodiment is provided, for example, with a stacked structure 60 where aplurality of insulating layers 44 and control gate electrodes 18 arealternately stacked on a silicon substrate 50. The insulating layer 44is, for example, a silicon oxide film. Further, the gate electrode 18is, for example, polycrystalline silicon doped with impurities to impartconductivity.

A hole is provided which penetrates the stacked structure 60 from itstop to the lowermost control gate electrode 18. The block insulatingfilm 16 is provided on the side surface of the hole, and the organicmolecular layer 14 is provided on the inner surface of the blockinsulating film 16. The block insulating film 16 is, for example,aluminum oxide (Al₂O₃).

Further, the tunnel insulating film 12 is provided on the inner surfaceof the organic molecular layer 14. The tunnel insulating film 12 is, forexample, a silicon oxide film.

Further, the columnar semiconductor layer 10 is formed on the innersurface of the tunnel insulating film 12. The semiconductor layer 10 is,for example, silicon.

In each of FIGS. 14 and 16, a region surrounded by a dashed line is thememory cell. The memory cell has a structure in which the tunnelinsulating film 12 is formed on the semiconductor layer 10, the organicmolecular layer 14 is formed on the tunnel insulating film 12, the blockinsulating film 16 is formed on the organic molecular layer 14, and thegate electrode 18 is formed on the block insulating film 16.

A method for manufacturing the nonvolatile semiconductor memory deviceaccording to the present embodiment includes: alternately depositing aplurality of insulating layers and control gate electrode layers on asubstrate to form a stacked structure; forming a hole that penetratesthe stacked structure from its top surface to the lowermost control gateelectrode layer; forming a block insulating film on the side surface ofthe hole; forming as a monomolecular film a first organic molecular filmwhich contains the first organic molecules having charge storing units,on the inner surface of the block insulating film by self-assembling;forming a second organic molecular film which contains second organicmolecules as amphiphilic organic molecules on the inner surface of thefirst organic molecular film; forming a tunnel insulating film on theinner surface of the second organic molecular film; and forming asemiconductor layer on the inner surface of the tunnel insulating film.

The tunnel insulating film 12 can be formed by using ALD (Atomic LayerDeposition), spin-coating or sputtering. A formation method where theorganic molecular layer 14 formed of the organic molecules is notdisassembled, damage is small and coverage inside the hole is high isdesirable, and for example, thermal ALD or spin-coating is desirable.

The tunnel insulating film 12 is formed on the second organic molecularfilm 14 b having hydrophilic properties. Hence the high-quality tunnelinsulating film 12 is formed.

When the insulating film after the film formation is annealed using aRapid Thermal Annealing (RTA) device, anatomic density in the filmincreases, which is desirable.

In the nonvolatile semiconductor memory device according to the presentembodiment, the high-quality tunnel insulating film 12 can be realizedby provision of the above configuration. This leads to an improvement ininsulation properties between the charge storing unit 26 b and thesemiconductor layer 10, thereby improving data retention properties(retention properties). This also leads to an improvement in reliabilityof the tunnel insulating film 12.

Further, according to the present embodiment, the memory cell is madethree-dimensional, to increase the integration degree of the memorycell, thereby allowing realization of a nonvolatile semiconductor memorydevice with a higher integration degree than those of the first to fifthembodiments.

Seventh Embodiment

The nonvolatile semiconductor memory device according to the presentembodiment differs in that the tunnel insulating film is not providedand the semiconductor is formed directly on the inner side of theorganic molecular layer. In the present embodiment, the organicmolecular layer also has the function of the tunnel insulating film.Hereinafter, descriptions of contents that overlap with those of thesixth embodiment will be omitted.

FIG. 14 is a three-dimensional conceptual diagram of the nonvolatilesemiconductor memory device according to the present embodiment. FIG. 17is an X-Y sectional view of FIG. 14. FIG. 18 is an X-Z sectional view ofFIG. 14.

The nonvolatile semiconductor memory device according to the presentembodiment is provided, for example, with the stacked structure 60 wherea plurality of insulating layers 44 and control gate electrodes 18 arealternately stacked on the silicon substrate 50. The insulating layer 44is, for example, a silicon oxide film. Further, the gate electrode 18is, for example, polycrystalline silicon doped with impurities andimparted with conductivity.

A hole is provided which penetrates the stacked structure 60 from itstop to the lowermost control gate electrode 18. The block insulatingfilm 16 is provided on the side surface of the hole. The blockinsulating film 16 is, for example, aluminum oxide (Al₂O₃).

The organic molecular layer 14 is provided on the inner surface of theblock insulating film 16. The organic molecular layer 14 is providedwith the first organic molecular film 14 a on the block insulating film16 side and the second organic molecular film 14 b on the semiconductorlayer 10 side.

Further, the second organic molecular film 14 b in the organic molecularlayer 14 also has the function of the tunnel insulating film.

The hydrophobic unit 27 a of the second organic molecule 27 contained inthe second organic molecular film 14 b contains straight chain saturatedhydrocarbon. Straight chain saturated hydrocarbon leads to improvementin insulation properties. The length of the straight chain is desirablynot smaller than 1 nm, and more desirably not smaller than 2 nm.

A main chain of the hydrophobic unit 27 a of the second organic molecule27 is, for example, an alkyl molecular chain. The alkyl molecular chainis, for example, an alkyl chain, an isoalkyl chain or a halogen alkylchain. The hydrophobic unit 27 a of the second organic molecule 27 maybe provided with a side chain.

For this reason, the carbon number of the alkyl molecular chain ispreferably not smaller than 8 and not larger than 30, and is moredesirably not smaller than 10 and not larger than 20. This is because,when the carbon number falls below the above range, the insulationproperties might deteriorate. Further, when the carbon number exceedsthe above range, the film thickness might become large, rendering thescaling-down being difficult.

Moreover, the columnar semiconductor layer 10 is formed on the innersurface of the organic molecular layer 14. The semiconductor layer 10is, for example, silicon.

In each of FIGS. 14 and 18, a region surrounded by a dashed line is thememory cell. The memory cell has a structure in which the organicmolecular layer 14 is formed on the semiconductor layer 10, the blockinsulating film 16 is formed on the organic molecular layer 14, and thegate electrode 18 is formed on the block insulating film 16.

A method for manufacturing the nonvolatile semiconductor memory deviceaccording to the present embodiment includes: alternately depositing aplurality of insulating layers and control gate electrode layers on asubstrate to form a stacked structure; forming a hole that penetratesthe stacked structure from its top surface to the lowermost control gateelectrode layer; forming a block insulating film on the side surface ofthe hole; forming as a monomolecular film a first organic molecular filmwhich contains the first organic molecules having charge storing units,on the inner surface of the block insulating film by self-assembling;forming a second organic molecular film which contains second organicmolecules as amphiphilic organic molecules on the inner surface of thefirst organic molecular film; and forming a semiconductor layer on theinner surface of the second organic molecular film.

The semiconductor layer 10 can be formed, for example, using CVD. InCVD, the organic molecular layer 14 formed of the organic moleculesmight be disassembled. For this reason, for example, it is desirable toform a thin oxide film of SiO₂ or the like having a thickness of about 1nm by ALD method, and thereafter form the semiconductor layer 10 on theinner surface of the oxide film by CVD.

In this case, the oxide film is formed on the second organic molecule ashaving hydrophilic properties, and the semiconductor layer 10 is formedon this oxide film. Therefore, a high quality oxide film is formed,thereby to suppress a damage on the organic molecular layer 14 caused bythe formation of the semiconductor layer 10.

According to the above embodiment, in place of the tunnel insulatingfilm of an inorganic material such as an oxide, the second organicmolecular film 14 b realizes the function of the tunnel insulating film.Therefore, the physical film thickness of the memory cell structure canbe small. Hence it is possible to realize the nonvolatile semiconductordevice provided with the fine memory cell.

Further, eliminating the need for formation of the tunnel insulatingfilm of the inorganic material can realize simplification of themanufacturing process.

EXAMPLE

In the following, an example will be described.

Example

A film structure corresponding to the first embodiment was created andevaluated.

Using a p-type silicon substrate, two-terminal element is produced bythe following method, and a pulse voltage is applied to write data, andcapacitance characteristics before and after the application aremeasured. It is thereby possible to check a charge storage amount andcharge retention time.

The p-type silicon substrate was introduced into a thermal oxidizationfurnace, to form a silicon oxide film on its surface. The thickness ofthe oxide silicon film was about 5 nm as a result of measuring the filmthickness. Next, using an ALD device, an aluminum oxide was formed to afilm on the oxide silicon substrate for only a cycle. A thickness of thealuminum oxide film was not larger than 1 nm.

Subsequently, the surface of the formed oxide silicon film wasirradiated to clean by a UV cleaner for ten minutes.

FIG. 19 is a diagram showing a molecular structure of a first organicmolecule used in the present example. The cleaned substrate was put intoa dehydrated toluene solution obtained by dissolving the first organicmolecules with the structure shown in FIG. 19 in a concentration of 1mM, and allowed to stand during a whole day and night.

Thereafter, the substrate was removed and transferred into pure toluene,and then rinsed while being stimulated by an ultrasonic cleaner for aminute. It is to be noted that this rinsing operation was performedtwice in total as toluene was replaced by a new one.

Thereafter, the substrate rinsed by toluene was transferred into pureethanol, rinsed while being stimulated by the ultrasonic cleaner for aminute, and then dried using an air duster.

Next, a solution obtained by dissolving pentaethyleneglycolmonododecylether as the second organic molecules in a concentration of 1mM in ethanol was spin-coated, and baked on a hot plate at 100° C. for90 seconds. Subsequently, the substrate was introduced into a thermalALD device, to form a hafnium oxide film on the second organic moleculesat 150° C. The thickness of the hafnium oxide film was about 10 nm as aresult of measuring the film thickness.

Then, the rear surface of the substrate was soaked in a hydrofluoricacid aqueous solution with a concentration of 0.5% to remove anunnecessary oxide film formed on the rear surface, and rinsed by purewater. Subsequently, aluminum was deposited on the rear surface, to givea substrate-side electrode.

Further, gold was deposited on the top surface of hafnium oxide of thesubstrate through a metal mask opened with a hollow, to give a controlgate electrode. Finally, it was introduced into the RTA device, andannealed under a N₂ gas atmosphere mixed with 3% of H₂ at 300° C. for 30minutes, to produce a two-terminal element.

Comparative Example

A two-terminal element was formed in a similar manner to that in theexample except that the second organic molecules were not formed buthafnium oxide was formed on the first organic molecules.

The aluminum electrode on the rear surface of each of the elementsaccording to the example and the comparative example was brought intocontact with a stage of a measurement device to take a terminal, and ameasuring needle was brought into contact with the gold electrode on thetop surface to take a terminal, and capacitance measurement wasperformed while a voltage was changed. Next, a pulse voltage was appliedto write data, and the capacitance measurement was performed again whilethe voltage was changed, to measure an amount of charges stored in goldnano particles.

FIG. 20 is a diagram showing results of the capacitance measurementbefore and after the pulse voltage application. It shows results ofperforming the capacitance measurement (initial measurement) on theelement of the example and then performing the capacitance measurementagain after applying a pulse voltage of −13V to the gold control gateelectrode on the top surface for an application time of 100 ms. Acapacitance saturated region was seen, and it was confirmed that athreshold voltage which is a voltage changing to the saturated regionshifted in a minus direction.

This voltage shift indicates that positive charges transfer to the firstorganic molecules represented in FIG. 19 from the p-type siliconsubstrate due to the pulse voltage applied from the gold control gateelectrode, and the positive charges are stored.

FIG. 21 is a diagram showing temporal changes of the capacitances. Thecapacitance measurement was performed at constant time intervals andvalues of the voltage changes were plotted with respect to the retentiontime.

The retention time for the stored charges can be evaluated by checkinghow much the value of the capacitance voltage shift has declined. Thetime in which the value of the voltage shift declined by 5% from thevalue measured immediately after the pulse application was determined.As shown in FIG. 21, it was found that the value did not decline by 5%within the measurement time in the case of the example.

When a similar measurement was performed in the comparative example, thetime taken for the 5%-decline was about 3.20 s as shown in FIG. 21, andhence it was found that the retention time for the stored charges waslonger in the case of the example than in the case of the comparativeexample. This is considered because introducing the second organicmolecules as the amphiphilic organic molecules leads to an increase indensity of the block insulating film as the hafnium oxide film formed bythe ALD method, thereby providing improved insulation properties.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, non-volatile semiconductor memorydevice described herein may be embodied in a variety of other forms;furthermore, various omissions, substitutions and changes in the form ofthe devices and methods described herein may be made without departingfrom the spirit of the inventions. The accompanying claims and theirequivalents are intended to cover such forms or modifications as wouldfall within the scope and spirit of the inventions.

What is claimed is:
 1. A nonvolatile semiconductor memory device,comprising: a semiconductor layer; a control gate electrode; and anorganic molecular layer formed between the semiconductor layer and thecontrol gate electrode, the organic molecular layer having a firstorganic molecular film on the semiconductor layer side containing firstorganic molecules, the organic molecular layer having second organicmolecular film on the control gate electrode side containing secondorganic molecules, the first organic molecule having a charge storingunit, the second organic molecule being an amphiphilic organic molecule.2. The device according to claim 1, wherein the amphiphilic organicmolecule contains straight chain saturated hydrocarbon.
 3. The deviceaccording to claim 1, wherein the amphiphilic organic molecule has ahydrophobic unit and a hydrophilic unit, the hydrophobic unit is analkyl chain, a fluoroalkyl chain, a polysilane chain or a phenylenechain, and the hydrophilic unit has one of an ether group, a carboxygroup, a hydroxy group, an amino group or a thiol group.
 4. The deviceaccording to claim 1, wherein the amphiphilic organic molecule ispolyethylene glycol alkylether shown in General Formula (I),

wherein, n is an integer not smaller than 3 and not larger than 20, andm is an integer not smaller than 3 and not larger than
 20. 5. The deviceaccording to claim 1, wherein the amphiphilic organic molecule istrisiloxanepolyethylene glycol shown in General Formula (II),

wherein, n is an integer not smaller than 3 and not larger than 20, andm is an integer not smaller than 3 and not larger than
 20. 6. The deviceaccording to claim 1, wherein the amphiphilic organic molecule ispentaethyleneglycol monododecylether.
 7. A nonvolatile semiconductormemory device, comprising: a stacked structure having insulating layersand control gate electrode layers, the insulating layers and the controlgate electrode layers being alternately stacked; a block insulating filmprovided on a side surface of a hole penetrating the stacked structurefrom its top surface to the lowermost control gate electrode layer withrespect to a stacking direction of the stacked structure; an organicmolecular layer having a first organic molecular film formed on an innersurface of the block insulating film containing first organic molecules,the organic molecular layer having a second organic molecular filmformed on an inner surface of the first organic molecular filmcontaining second organic molecules, the first organic molecule having acharge storing unit, the second organic molecule being an amphiphilicorganic molecule; a tunnel insulating film provided on the inner surfaceof the organic molecular layer; and a semiconductor layer provided onthe inner surface of the tunnel insulating film.
 8. The device accordingto claim 7, wherein the amphiphilic organic molecule has a hydrophobicunit and a hydrophilic unit, the hydrophobic unit is an alkyl chain, afluoroalkyl chain, a polysilane chain or a phenylene chain, and thehydrophilic unit has one of an ether group, a carboxy group, a hydroxygroup, an amino group or a thiol group.
 9. The device according to claim7, wherein the amphiphilic organic molecule is polyethylene glycolalkylether shown in General Formula (I),

wherein, n is an integer not smaller than 3 and not larger than 20, andm is an integer not smaller than 3 and not larger than
 20. 10. Thedevice according to claim 7, wherein the amphiphilic organic molecule istrisiloxanepolyethylene glycol shown in General Formula (II),

wherein, n is an integer not smaller than 3 and not larger than 20, andm is an integer not smaller than 3 and not larger than
 20. 11. Thedevice according to claim 7, wherein the amphiphilic organic molecule ispentaethyleneglycol monododecylether.